To be able to understand and improve various optical systems including fs-laser lightsources, we developed a numerical simulation based on the coherent transfer function (CTF). Our work created a simulation tool, which is able to simulate all three dimensions and time while accounting for coherent light, short pulses, aberrations, chirp, pulse delay, numerical aperture, the intensity distribution and the polarization of the incident light. We explain the theoretical approach and aspects necessary for the simulations. Then we show the capabilities of our tool in simulation aberrations, 4Pi point spread functions, two objective fs-pulse interaction and multi objective confocal fluorescence microscopy.